M.A.P.

Hi Sean,
I hope that this helps to elaborate on what Airmaster has told you:

For the purposes of this reply, I will assume that the Airmaster controller is in AUTO/CRUISE mode with the factory setting of 5000 RPM, and everything is functioning as it should.

If opening the throttle results in the engine speed increasing past 5000 RPM, this indicates that the prop has reached its coarse pitch limit and the controller is therefore unable to command the prop to add any more load on the engine. Because at this point any increase in airspeed will reduce the angle of attack of the prop, the only way to increase the MAP without an accompanying increase in engine speed is to absorb the excess power in some other way, for example by climbing.

In essence what the figures you have quoted are telling me is that your airframe is slippery enough that your prop reaches full coarse at less than 75% power in level flight.

If you want to cruise at 75% power while using the Rotax recommended combination of RPM and MAP, you need to increase the setting of the coarse pitch limit switch in the propeller's hub so the controller has enough authority to keep the engine speed under control. Just be aware that increasing the prop's coarse pitch limit can have safety implications in the event of a prop or controller failure.

Sean Griffin wrote:

If I understand (?) Airmasters advice;

 # Adjust the Controller programing to give Auto Cruise of 5000 rpm at WOT ie when I switch from Climb, to Cruise, the pitch change (coarsen) to the prop, will deliver (governed) 5000 rpm

 # I can then adjust power/throttle to achieve Rotax recommended/desired MAP.

No! You do NOT change the controller programming (unless it has already been set wrong).

You adjust the coarse limit stop microswitch as per the manual, including the final safety check to make sure you can still climb away from a baulked landing if the prop fails at full coarse.

See manual section 8.3.2, in summary -

Aircraft tied down. Controller in MANUAL mode, with the rocker switch set prop to fully coarse. See what rpm you get at WOT (MAP will be 28 or so.) You want about 4000 rpm. (Based on what you have said, you'll probably get over 5000!)

If rpm is much more or less than 4000, adjust the coarse pitch stop microswitch and try again. It's fiddly.

BTW how are you measuring rpm? The Rotax dial instrument (the one made by Aviasport) has a poor reputation e.g. mine agrees with my MGL digital readout at 5700 but at lower speeds disagres by up to 400rpm. I assume the MGL being digital pulse counting is accurate.

Just so I am not misquoting/understanding Airmaster advise, this is the letter I wrote with answers:

">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

My usual (Auto) practise is as follows;

• TO: Max power (WOT)/RPM 5750 – not much concerned with MAP
• Climb: Max power (WOT) /RPM5450 – not much concerned with MAP
• Cruise Max power (WOT)/RPM 5450 – reduce rpm by reducing power/throttle to somewher between 5000 – 5300 rpm (130-137 knots). As I am interested in economy, I am usually around 5000-5100 rpm.

Please check the setting for Cruise is 5000 https://www.propellor.com/ac200-user-software-tool

In this step you should select Cruise (blue knob).  RPM will drop to 5000.

Reduce throttle to the map you desire

Rotax say I should have a MAP of around 27.2” but I see 26.2” (depending on Alt see table).

If I increase power – I also increase rpm & fuel consumption.

Perhaps I should start using the Hold function – will this allow reduction in power while maintaining rpm?

Not sure, if I record rpm against WOT, from 5000 – 5450, I will see MAP always lower than Rotax figures

>>>>>>>>>>>>>"

I responded - yet to receive an answer;

">>>>>>>>

Am I to understand, that your advice is to adjust  the computer settings, so that when I select Auto Cruise, the prop RPM will be automatically  governed (by pitch change/setting) to 5000 rpm?

If I do this, will it then limit pilot, in flight, choice for higher speed cruise?

>>>>>>"

Hi Gentlemen,

First - my sincere thanks, for persevering with what must seem to you guys to be "not the sharpest tool in the shed"

Tim;

I think I understand where you are coming from - Basically Airmaster advice.

See my question, back to Airmaster, about pilot inflight options, once this instruction has been acted on.

Mike;

A, pre first Test Flight, static test has been done and found to meet Airmaster standards/instructions. However it may be prudent to do this again, to double check results.